Internal combustion engines can operate with a low fuel consumption and no-smoke exhaust only in case of an effective mixing, i.e. an effective formation of the combustible fuel-air mixture. In order to intensify the process of evaporation and mixture formation of the fuel injected into the cylinder use is made of the vortex movement of the air charge with respect to the combustion chamber walls.
Most widely used for mixture formation is a vortex movement of the air charge, directed tangentially with respect to the lateral sides of the combustion chamber and produced by a device provided in the inlet member, during the suction process. The tangential vortex movement of the air charge makes it possible to organize a stable mixture formation as well as a uniform concentration of fuel vapours throughout the combustion chamber volume in case of a non-uniform distribution of fuel sprays by the injection nozzle in combustion chamber volume. This contributes to the wide application of the tangential movement of the air-charge in small-size engines with two-valve cylinder heads and, consequently, with injection nozzles displaced from the cylinder axis.
A typical engine wherein a tangential movement of the air charge is used for mixture formation, is a diesel engine according to the British Pat. No. 1,167,015 published Oct. 15, 1969. The engine comprises a combustion chamber provided in a piston, the centre of the combustion chamber coinciding with or being disposed near the axis of the cylinder. The combustion chamber is so arranged that when the piston is in the top dead centre position at the end of the compression stroke, almost all of the combustion air is disposed in the chamber. Means are provided for producing, during the suction stroke, the rotational movement of the combustion air in a vortex around the axis of the combustion chamber. The injection nozzle is displaced from the axis of the chamber and has at least two discharge openings, or fuel spray outlets, spaced above the maximum diameter of the combustion chamber, with the piston in the top dead centre position. The injection nozzle discharges fuel sprays of different lengths, the sprays being directed toward the cylinder axis, and extending substantially transversely to the vortex in the combustion chamber and not spraying over the edge of the combustion chamber opening. A part of the injected fuel strikes against the combustion chamber wall surface and a part of the injected fuel is distributed in the combustion air of the combustion chamber. One of the fuel sprays, the longest one, is directed towards the combustion chamber side wall and initiates the ignition of the fuel, while the other or others have an opposite direction so that they impinge on the combustion chamber side wall where the fuel injection nozzle is arranged at approximately the same height, at which the longest fuel spray hits the middle part of the combustion chamber side wall. In case the injection nozzle has at least three fuel spray outlets, the projections thereof upon the plane perpendicular to the cylinder axis are disposed asymmetrically with respect to the diametral plane extending through the axis of the combustion chamber and the injection nozzle axis. If the injection nozzle has only two fuel spray outlets, the axes of the same are situated in the diametral plane extending through the combustion chamber axis and the injection nozzle axis. In said engine the intersection point of the axes of the injection nozzle fuel spray outlets is spaced from the combustion chamber axis at a distance equal to at least one fifth of the maximum diameter of the combustion chamber. Positioning of the injection nozzle eccentrically with respect to the combustion chamber axis in said engine makes it possible to arrange inlet and outlet valves as well as inlet and outlet ports of sufficient cross sections. Owing to the central arrangement of the combustion chamber a uniform temperature is provided in the vicinity of the annular grooves in the pistons. In said engine the direction of the fuel sprays is such that no spray adversely affects another spray which may be caused by the vortex motion of the air charge, whereby optimum conditions are provided for producing the fuel mixture.
However, in said engine like in all other engines with the tangential rotation of the air charge, the rotational movement of the air charge in the combustion chamber attenuates with the piston moving downward from the top dead centre position at the beginning of the expansion stroke, when, in the supercharge-rated engine, the processes of the fuel injection and combustion are not completed yet. In this case both the intensity of mixture formation and the homogeneity of distribution of the fuel vapours throughout the combustion chamber volume are impaired. The rotational movement ceases at the instant when the rotation should still continue so as to increase the combustion efficiency. Attempts to raise the rotational speed of the air charge in order to prolong the action of the tangential currents result in a higher pressure drop in the inlet members, thus reducing the filling of the cylinder with a fresh air charge. Besides, high speeds of the vortex at the beginning of the injection may adversely affect the conditions of the fuel self-ignition and result in a more rough operation of the engine.
It has been proposed to apply, for the purposes of mixture formation, the vortex movement of the air charge in the radial direction with respect to a specially inclined side wall of the combustion chamber. The vortex movement arises when the air charge is forced from the cylinder volume into the chamber in the piston, the latter moving towards the upper position at the end of the compression process, and the air charge and combustion products pass in the reverse direction as the piston moves downwards at the beginning of the expansion process. The vortex movement in the radial direction is most effective in case of the uniform distribution of the fuel sprays throughout the combustion chamber volume, as the tangential components of the air charge velocity appearing with a non-uniform distribution of the fuel sprays throughout the combustion chamber volume are unable of displacing the fuel in the combustion chamber volume in the tangential direction and equalize the concentration of its vapours. Therefore, the formation of the mixture by means of the radial movement of the air charge is used mainly in engines having their injection nozzle disposed centrally with respect to the combustion chamber, the fuel sprays being dispersed uniformly with respect to the injection nozzle and the chamber, the radial currents occurring throughout the combustion chamber.
In engines with two-valve cylinder heads no space is provided for arranging the injection nozzles, therefore, the injection nozzles are spaced from the cylinder axis and disposed eccentrically with respect to the combustion chamber in the piston. In this case the impaired mixture formation resulting from the displacement of the injection nozzle is compensated for by a sufficient passage section of the valves and outlets, as well as by simple design of the cylinder head.
A typical engine with a two-valve cylinder head and an injection nozzle displaced with respect to the cylinder axis, wherein use is made of the radial vortex movement of the air charge, is the internal combustion engine described in the book "Operation of Diesel Engines with the Chamber in the Piston" (N. N. Ivanchenko and others, 1972, Mashinostroenie Leningrad, pp. 23-25; 29-36). The engine comprises a chamber in a piston, the chamber having a conical side wall tapering toward the throat, and an injection nozzle with a plurality of fuel spray outlets symmetrically and uniformly spaced with respect to the injection nozzle axis for injecting the fuel onto the side wall of the combustion chamber disposed in the cylinder head with the eccentricity from 0.1 to 0.25 of the combustion chamber throat radius. The optimum relationship of the volume of the combustion chamber in the piston to the total volume of the combustion chamber is at least 0.78-0.80, the optimum diameter of the throat being 0.35-0.37 of the cylinder bore. The volume-film mixture formation in the engine is accomplished by acting on the fuel sprays and fuel films applied onto the combustion chamber walls of radial air streams and small-scale turbulent vortex, these being produced in the course of forcing the air charge out of the cylinder volume into that of the chamber in the piston, when the piston moves in the upward direction at the end of the compression process, at the instant of the injection nozzle injecting the fuel into the cylinder, and the air charge and combustion products passing in reverse direction, out of the volume of the combustion chamber in the piston into the cylinder volume when the piston moves downward at the beginning of the expansion process. In said engine the movement of the air charge occurs during the entire fuel injection process, thus raising the efficiency of the mixture formation and fuel combustion in the supercharged engines.
However, in said engine, as well as in other engines of this kind, there takes place a non-uniform distribution of the fuel throughout the combustion chamber volume and relative to radial streams, thus causing a non-uniform concentration of the fuel and its vapours in the combustion chamber. In the engine the mixture formation and the combustion of a part of the fuel injected by the nozzle in the direction of the combustion chamber side wall closest thereto occur in a disproportionally smaller part of the air charge as compared to the mixture formation and combustion of the portion of the fuel injected in the direction of the combustion chamber wall situated farther from the injection nozzle, thus considerably impairing the efficiency of the mixture formation and combustion of the whole fuel injected into the cylinder. In case of the higher supercharge ratings, i.e. the increased cyclic fuel deliveries, the radial streams alone are not sufficient for the effective mixing of the fuel sprays non-uniformly dispersed throughout the combustion chamber, whereas the application of conventional methods of "vortexing" the stream in the tangential direction results in additional pressure losses during the admittance of the air into the cylinder. Besides, the longer flames in case of the increased cyclic fuel injections, accomplished at the equal angles with respect to the injection nozzles, are distributed in the combustion chamber space in such a manner that the combustion products when passing from the chamber in the piston into the cylinder volume intersect the fuel flames and prevent the fresh air from getting to the fuel, thus impairing the mixture formation and combustion. The decreased amount of air introduced into the combustion space increases the temperature as well as thermal stresses in the chamber walls thus causing cracks in the chamber throat edges.